1. Field of the Invention
The present invention relates to a phosphor used in a display device such as CRT, PDP, FED, and EL, and a lighting device and so on, such as a vacuum fluorescent display and a fluorescent lamp. Especially it relates to the phosphor which is excited by ultraviolet light to visible light to emit visible light or white light, an LED, and a light source using the phosphor.
2. Description of the Related Art
Currently, a discharge fluorescent lamp, a filament lamp, and so on used as lighting devices have various problems such as containing harmful substances like mercury or the like, having a short life span, and so on. However, in resent years, LEDs emitting a blue or ultraviolet light are developed one after another. The ultraviolet to blue lights emitted from the LED are combined with a phosphor having an excitation band within a ultraviolet to blue wavelength region, and thereby a white light is obtained by mixing the LED emitting light and emission of the phosphors. Then, researches and developments to utilize the white light as a lighting of the next generation are being conducted vigorously. This white LED lighting has advantages such as the amount of heat generation is small, the life span is long without being broken like a conventional filament lamp because it is constituted from a semiconductor element and the phosphor, and the harmful substance such as mercury is not necessary, so that it is an ideal lighting device.
Here, to obtain white light by the combination of the above-described LED and the phosphor, two modes are considered in general. One mode is to combine an LED emitting blue light and a phosphor excited by receiving the blue light emission to emit yellow light, and by the combination of blue light emission and yellow light emission, white light emission is obtained.
The other mode is to combine an LED emitting a near-ultraviolet or ultraviolet light, and a phosphor excited by receiving the near-ultraviolet or ultraviolet light emission to emit a red (R) light, a phosphor emitting a green (G) light, a phosphor emitting a blue (B) light, and other colors, and thereby obtaining white light emission by RGB and other color lights. This method to obtain white light emission by using RGB and other color lights has a wide range of application as a lighting device because any light emitting color other than white light can be obtained by the combination and the compounding ratio of RGB and other color phosphors. As phosphors used for this purpose, there are red phosphors of, for example, Y2O2S:Eu, La2O2S:Eu, 3.5MgO.0.5MgF2.GeO2:Mn, and (La, Mn, Sm)2O2S.Ga2O3:Eu, green phosphors of, for example, ZnS:Cu, Al, SrAl2O4:Eu, and BAM:Eu, Mn, a yellow phosphor of, for example, YAG:Ce, and blue phosphors of, for example, BAM:Eu, Sr5(PO4)3Cl:Eu, ZnS:Ag, (Sr, Ca, Ba, Mg)10(PO4)6Cl2:Eu. And those RGB and other color phosphors are combined with light emitting portions such as the LED and so on emitting a near-ultraviolet or ultraviolet light in an attempt to obtain a light source or a lighting device such as the LED and so on which emits white or a desired light.
However, as for the white LED lighting by the combination of blue LED and the yellow phosphor (YAG:Ce), the light emission at the long wavelength side in the visible light region is in shortage, so that the white light emission becomes slightly blue-tinged, and the somewhat red-tinged white light emission like an electric bulb cannot be obtained.
Besides, in the white LED lighting by the combination of near-ultraviolet or ultraviolet LED, and RGB and other color phosphors, the excitation efficiency on the long wavelength side of the red phosphor is not good compared to the other phosphors within the three color phosphors, so that the emission efficiency is low. Therefore there is no other choice than to increase the compounding ratio of only the red phosphor, and the phosphor to increase the luminance is in shortage, so that the white light with high luminance cannot be obtained. Furthermore, the emission spectrum of the phosphor is sharp, so that there is a problem that the color rendering properties of the obtained light is not good.
Therefore, recently, an oxynitride glass phosphor (for example, refer to Patent Document 1) having a good excitation on the long wavelength side and obtaining a light emitting peak with a wide half value width, a phosphor having a sialon as a host material (for example, refer to Patent Documents 2 and 3), and a phosphor containing nitrogen such as silicon nitride group or the like (for example, refer to Patent Documents 4 and 5) are reported. Since the phosphor containing nitrogen has more covalent bonding ratio compared to the oxide type phosphor, the phosphor has a characteristic of having a good excitation band for the lights having 400 nm wavelength or more, and it comes under the spotlight as the phosphor for the white LED.
[Patent Document 1] Japanese Patent Application Laid-open No. 2001-214162
[Patent Document 2] Japanese Patent Application Laid-open No. 2003-336059
[Patent Document 3] Japanese Patent Application Laid-open No. 2003-124527
[Patent Document 4] Translated National Publication of Patent Application No. 2003-515655
[Patent Document 5] Japanese Patent Application Laid-open No. 2003-277746